Wireless radio access technologies continue to be improved to handle increased data volumes and larger numbers of subscribers. The 3GPP organization is developing a new radio system (commonly referred to as NR or 5th Generation/5G) to handle peak data rates of the order of ˜10 Gbps (gigabits per second) while still satisfying ultra-low latency requirements in existence for certain 4G applications. 5G intends to utilize radio spectrum on the order of GHz or more in the millimeter-wave (mmWave) band; and also to support massive MIMO (m-MIMO). M-MIMO systems are characterized by a much larger number of antennas as compared to 4G systems, as well as finer beamforming and a higher antenna gain. Analog beamforming and/or hybrid beamforming architectures containing both analog and digital beamforming will be utilized at least in certain m-MIMO scenarios operating in the mmWave band.
FIG. 1 is a schematic overview of an example 50 radio environment in which these teachings may be deployed. Rather than a conventional unitary cellular base station/eNB the 5G system is to have the conventional base station's functionality distributed among a baseband unit (BBU) 20 (which may be implemented as a single BBU or multiple interconnected BBUs) and one or typically multiple remote radio heads (RRHs) 30 each located up to a few kilometers from the BBU 20. Each RRH 30 is operationally connected to its BBU 20 via a wired or wireless bidirectional transmission link 25 referred to as a front haul (FH) link. Currently the BBU/RRH combination in 5G systems is referred to as a gNB. The UE 10 is in direct communication with one or more of the RRHs 30, which in the 5G system each RRH 30 would be operating as a transmission/reception point (TRP) of the gNB. The UE 10 may have active connections to more than one RRH 30, shown in FIG. 1 as two TX/RX beam pairs with two different TRPs/RRHs. There is a somewhat similar distribution of access node functionality in cloud-based radio access networks (C-RAN) that are currently being deployed at least for some LTE-based networks, though those systems typically use a different terminology than BBU and RRH.
Beam blockage becomes an acute concern at mmWave frequencies, and downlink control channels in particular need robustness against such blockages. In general narrow beams between transmitter and receiver are more sensitive to blockage than wide or omnidirectional beams. Each TRP within a cell may perform beam sweeping to enable UEs to detect and measure potential transmit beams, for example for downlink control (NR-PDCCH) and shared data channels (NR-PDSCH). Different UEs may of course have different beamforming capabilities, for example a given UE may be able to receive using one or using multiple RX beams at a time. Providing connection to UE from multiple TRPs within a cell provides diversity against sudden beam blockages.
Consider the PDCCH which can schedule multiple UEs for uplink or downlink resources for communicating data. A given UE has a prescribed window in which to listen for a PDCCH addressing it, and if this UE does not see its own identifier in a given PDCCH that means this PDCCH does not schedule resources for this UE. This operation may be referred as PDCCH blind detection. In this case the UE would not signal the network to confirm it read the PDCCH that did not schedule it. But if instead a given PDCCH did schedule the UE and the UE did not properly receive it, for example due to blockage of the beam that was to carry it, the UE would also not signal the network for it does not know it missed a PDCCH. In the latter case the network would eventually recognize this because the UE would either not send data on its scheduled uplink resource, or would not acknowledge data sent to it on the scheduled downlink resource. But this is too long of a delay, particularly in a NR/5G type radio environment where the viable beams for a UE may change rapidly. Embodiments of these teachings utilize that PDCCH, or more generally control channel signaling, so that the UE and the network can recognize beam disruptions sooner.
Some relevant teachings may be seen at the following documents.                R1-1612863 by Nokia, Alcatel-Lucent and Shanghai Bell entitled Beam management—DCI monitoring [3GPP TSG-RAN W1#87; Reno, US; 14-18 Nov. 2016].        R1-1701089 by Nokia, Alcatel-Lucent and Shanghai Bell entitled Beam management—DCI monitoring [3GPP TSG RAN WG1 NR Ad-Hoc Meeting; Spokane, US; 16-20 Jan. 2017].        R1-1701093 by Nokia, Alcatel-Lucent and Shanghai Bell entitled Multi-beam control channel transmission [3GPP TSG RAN WG1 NR Ad-Hoc Meeting; Spokane, US; 16-20 Jan. 2017].        R1-1701011 by Nokia, Alcatel-Lucent and Shanghai Bell entitled On the PDCCH search space structure for NR [3GPP TSG-RAN WG#NR; Spokane, US; 16-20 Jan. 2017].        US patent application publication 2016/0150435 by Beak t al. entitled Communication Method and Apparatus Using Beamforming [published 26 May 2016].        International patent application serial number PCT/EP2015/070926 [by Nokia Technologies Oy, and published as WO/2017/045694, published on Mar. 23, 2017].        